1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a manufacturing method of the same.
2. Description of the Related Art
FIG. 7A to FIG. 7C show a configuration of a conventional solid electrolytic capacitor. FIG. 7A is a sectional side view, FIG. 7B is a sectional front view, and FIG. 7C is a bottom view, respectively. FIG. 7A shows a sectional view taken along line 7A-7A of FIG. 7C, and FIG. 7B shows a sectional view taken along line 7B-7B of FIG. 7C.
Capacitor element 61 includes anode body 62, anode leader 63, dielectric oxide film 64, solid electrolyte 65, and cathode layer 66. Anode body 62 is formed of a valve metal foil. Anode leader 63 is provided at one end of anode body 62, and dielectric oxide film 64 is formed on a surface of another end of anode body 62. Solid electrolyte 65 made of a conductive polymer is provided on dielectric oxide film 64. In cathode layer 66, a carbon layer is laminated on solid electrolyte 65, and a silver paste layer is laminated on the carbon layer.
Anode terminal 67 and cathode terminal 68 are formed of metal plates which are made by machining copper lead frames. Anode terminal 67 includes flat portion 70, leading portions 72, and placement portions 74. Flat portion 70 is exposed from outer casing resin 69 at mounting surface 76. Leading portions 72 are bent obliquely upward from both ends of flat portion 70. Placement portions 74 are coupled with a lower surface of anode leader 63. Cathode terminal 68 includes flat portion 71, leading portions 73, and placement portions 75. Flat portion 71 is exposed from outer casing resin 69 at mounting surface 76. Leading portions 73 are bent obliquely upward from both ends of flat portion 71. Placement portions 75 are coupled with a lower surface of cathode layer 66.
Outer casing resin 69 is made of an electrically insulating resin such as an epoxy resin. Outer casing resin 69 covers capacitor element 61 such that anode terminal 67 and cathode terminal 68 are exposed in the same plane with mounting surface 76 in the flat shape.
In the above mentioned configuration, anode terminal 67 and cathode terminal 68 are provided such that anode terminal 67 and cathode terminal 68 are arranged adjacent to each other as close as possible, which shortens a path of current passing through capacitor element 61 from wiring of a circuit board. Therefore, equivalent series resistance (ESR) and equivalent series inductance (ESL) are decreased in the solid electrolytic capacitor. For example, Japanese Patent Unexamined Publication No. 2003-133177 discloses this kind of solid electrolytic capacitor.
The state in which the conventional solid electrolytic capacitor is mounted on the circuit board will be described with reference to FIG. 8. FIG. 8 is a sectional view showing a mounted state of the solid electrolytic capacitor shown in FIG. 7A. Lands 78 are provided in circuit board 77. Lands 78 correspond to positions of anode terminal 67 and cathode terminal 68 which are exposed at mounting surface 76, and lands 78 have shapes substantially similar to those of the terminals. After a solder cream is applied onto lands 78, the solid electrolytic capacitor is placed on lands 78, and the solder is melted by high-temperature reflow to join the solid electrolytic capacitor to circuit board 77. At this point, when an area of cathode terminal 68 in mounting surface 76 is larger than that of anode terminal 67, the melted solder is easily aggregated in a central portion of cathode terminal 68. Therefore, soldering layer 79A on anode terminal 67 differs from soldering layer 79B on cathode terminal 68 in thickness, which sometimes results in a problem that mounting property is impaired such that the solid electrolytic capacitor is mounted while inclined or floating.